However, you probably won’t. Metabolic damage can happen to those who have an extremely restricted daily caloric intake (we’re talking less than 1000 calories per day) combined with doing 2-3 hours of cardio per day. Those who develop the condition will likely have less than 10% body fat, and most people (thankfully) just never reach that point. Cardio bunnies and dieters, pay attention.

Jocelyn Hsu

So, what is metabolic damage?

Rather than the simple calories in vs. calories out math equation that most people think it is, the metabolism is like a thermostat or a see-saw always trying to find balance. The metabolism is made up of multiple systems: the nervous system, the endocrine system, the digestive system, and the immune system. Sounds complicated, right? Because it is. These systems overlap, which is why it’s actually kinda hard to speed up your metabolism.

According to this article written by an integrative physician, metabolic damage occurs when these systems’ functions become compromised. It is rare, gradual, and similar to falling dominoes. Once one falls, so does the next if your lifestyle doesn’t change.

Nervous System Function

The nervous system has a sympathetic side and a parasympathetic side. The sympathetic system is the side of the seesaw activated by stress, known as the “fight or flight” system. The parasympathetic system is the calm side of the see-saw, called the “rest and digest” system.

Some stress is normal, like during exam time, but if you’re constantly putting your body through the stresses of extreme low-calorie dieting and heavy daily cardio, your nervous system can get stuck on the sympathetic side of the seesaw, even when you’re not exercising. This represses your parasympathetic system, and then your body cannot digest food well, so you become malnourished (along with some other symptoms of being under constant stress like not sleeping well and having a higher resting heart rate).

Endocrine System Function

This is the hormonal part of the metabolism. It’s controlled by the hypothalamus and the pituitary gland (the HP). When your nervous system is stuck in a constant stressed-out state, your HP sends more hormonal signals to the adrenal, thyroid, and the gonads than normal, which makes them also produce extra hormones, which makes the HP produce even more hormones (sounds even worse than the time of the month, huh?). If the flow of hormones is too strong for too long then cells all over the body can lose their receptiveness to them, which is called hormone resistance.

Other Functions

After the nervous and the endocrine systems stop functioning as they should, the digestive system, the immune system, and the reproductive system suffer. Once these last dominoes fall, your metabolism adapts to not needing to burn calories and it has major difficulty doing so when it is reintroduced to them, even years after the initial calorie restriction. This article shows that the winners from the show “The Biggest Loser” often end up with extremely low metabolisms as a result of crash dieting even years later, which makes them regain weight.

Those with metabolic damage usually have these symptoms:

- Multiple digestive complaints (IBS, bloating, gas, etc.)

- Depression

- Dry skin, itchy scalp, slow thinking

- Susceptible to illness

- A puffy/waterlogged look

- Exhausted and no motivation

- Low libido

- Irregular or completely absent period

- Lightheadedness

- New sensitivity to bright lights

- Multiple food intolerances

- Continual fatigue

- Mood changes

- Dysfunctional sleep

- Inability to lose weight/weight gain

Don’t be too quick to panic. Many people hear about metabolic damage and think that they have it just because they cannot lose weight anymore, but that’s more like metabolic resistance or compensation, which you can read about here. You won’t damage your metabolism in a matter of days or a few weeks, it happens when your body is pushed to its limits for months.

There is a lot of debate about whether or not metabolic damage actually exists. Some internet health gurus say that it is a myth, but from what I’ve read, these are the people that define it as not being able to lose weight or having a lower metabolic capacity. In functional medicine, it is called neuroedocrineimmune dysfunction, and it’s more than just not losing weight anymore.

Extreme athletes, anyone who loses weight for competitions, and anyone else who may have mixed extremely low-calorie diets with way too much cardio for repeated or extended amounts of time should be aware of the condition and the warning signs, and they should also know that there is recovery, which you can read about here and here. The process is long and hard, but still possible.